The present invention relates generally to method and apparatus for conducting a brain function diagnostic test and, more particularly, to such method and apparatus which can be used to accurately and repeatedly measure a subject's brain waves during electroencephalography.
An electroencephalograph (EEG) is a clinical, multichannel instrument used to measure and display the brain waves of a subject. The subject's brain waves are monitored in such an EEG by the use of a number of individual electrodes which are attached to the scalp of the subject in a predetermined pattern or montage which is well known in the art. The electrical activity (brain waves) generated by the subject's brain are detected by these electrodes and transmitted to external monitoring devices where they are amplified and displayed for viewing and diagnostic interpretation.
In the early years of EEG testing, the brain waves were displayed using a multichannel recorder with each trace made by a galvanometer-type pen motor. More recently, however, the EEG systems employ a microcomputer into which the brain waves are fed for analysis and display on the computer's accompanying CRT. The computer automatically records, analyzes and artifacts the EEG and prepares a detailed report with the tracing of the EEG. Through the use of the computer's analysis of the brain waves, it is now possible to graphically "map" the brain on the computer's CRT to check for abnormalities relative to an appropriate reference data base.
EEG testing is used not only to detect abnormalities in brain function but, in addition, for therapeutic monitoring of central nervous system (CNS)-effective drugs such as, for example, anti-epileptics, cerebrovascular compounds, psychotropics, etc. EEG testing has also been used clinically to determine the CNS toxicity of peripheral drugs such as cardiovascular drugs, antidepressants, anxiolytics, antihistamines and analgesics; to select the right psychotropic for a particular patient; and to determine the development of a progressive cerebral illness by repetitive quantitive EEG testing.
In research, EEG testing has been used to establish quantitative CNS effects of drugs after single or multiple doses, for classifying psychotropic properties of drugs; for predicting the "therapeutic window" of phychotropics; and for determining the potency of CNS-effective drugs and determining appropriate dose levels.
Representative of current EEG systems include those systems described, for example, in U.S. Pat. Nos. 3,518,986 which issued on July 7, 1970 to T. C. Woods et al. for Patient Monitoring Safety System; U.S. Pat. No. 3,859,988 which issued on Jan. 14, 1975 to C. C. Lencioni, Jr. for Open Lead Testing System for EEG; U.S. Pat. No. 4,202,354 which issued on May 13, 1980 to L. B. Smith et al; U.S. Pat. No. 4,213,465 which issued on July 22, 1980 to G. Renheim for Electroencephalograph; U.S. Pat. No. 4,214,591 which issued on July 29, 1980 to K. Sato et al. for Brain Wave Analyzing System and Method; U.S. Pat. No. 4,235,511 which issued on Dec. 2, 1980 to P. J. Loeb for Electroencephalograph; U.S. Pat. No. Re. 30,502 which issued on Feb. 3, 1981 to C. C. Lencioni, Jr. for Open Lead Testing System for EEG; U.S. Pat. No. 4,409,987 which issued on Oct. 18, 1983 to R. A. McIntyre for Electroencephalograph; U.S. Pat. No. 4,411,273 which issued to E. R. John on Oct. 25, 1983 for System and Method for Electrode Pair Derivations in Electroencephalography; and U.S. Pat. No. 4,424,816 which issued on Jan. 10, 1984 to A. S. Callahan et al. for Neurological Monitoring Device Test Circuitry.
Despite the sophistication of current EEG testing systems and their related computer hardware and software, the weakest link in all of these systems is the placement and securing of the individual electrodes to the subject's scalp. Nineteen individual electrodes must be located and specifically placed on a subject's scalp and good electrical contact must be established between the electrode and the subject's scalp. Current practice utilizes highly conductive, miniature "cup" shaped electrodes which are fastened to the subject's scalp by means of an adhesive type electrically conductive paste or cream. Placement of such electrodes is determined based on head measurements taken by the technician conducting the test in accordance with the International 10-20 system.
Examples of such prior art electrodes include those electrodes which are described in U.S. Pat. Nos. 2,872,926 which issued on Feb. 10, 1959 to J. E. Alderman for Electroencephalographic Electrode; U.S. Pat. No. 3,151,619 which issued on Oct. 6, 1964 to G. H. Sullivan for Electrode for Electromedical Equipment; U.S. Pat. No. 3,170,459 which issued on Feb. 23, 1965 to C. G. Phipps et al. for Bio-Medical Instrumentation Electrode; U.S. Pat. No. 3,187,745 which issued on June 8, 1965 to J. N. Baum et al. for Electrodes; U.S. Pat. No. 3,295,515 which issued on Jan. 3, 1967 to A. R. Kahn for Electrode Assembly; U.S. Pat. No. 3,469,577 which issued on Sept. 30, 1969 to J. A. R. Kater for Scalp Contacting Bioelectrode; U.S. Pat. No. 3,528,408 which issued on Sept. 15, 1970 to B. Opperman for Chemical Adhesive Electrode; U.S. Pat. No. 3,580,239 which issued on May 25, 1971 to H. Watanabe et al. for Method and Apparatus for In Vivo Potentiometric Measurements; U.S. Pat. No. 3,602,216 which issued on Aug. 31, 1971 to L. H. Moe, Jr. for Paste Dispensing Body Electrode; U.S. Pat. No. 3,623,479 which issued on Nov. 30, 1971 to C. C. Day for ECG Electrode with Partition; U.S. Pat. No. 3,669,110 which issued on June 13, 1972 to G. M. Low et al. for Compressible Biomedical Electrode; U.S. Pat. No. 4,033,334 which issued on July 5, 1977 to J. C. Fletcher et al. for Snap-In Compressible Biomedical Electrode; and U.S. Pat. No. 4,051,842 which issued on Oct. 4, 1977 to P. M. Michael et al. for Electrode and Interfacing Pad for Electrical Physiological Systems.
As a review of these patents will demonstrate, the state of the art relative to electrode design and placement has not advanced nearly as far as that of the related hardware and software used in analyzing the EEG results. Location and placement of the electrodes remains still a trial and error technique. Placement and securing of the 19 electrodes to the subject's scalp is a cumbersome, messy and time consuming method which requires a degree of training. The amount of time required to properly locate and connect the electrodes at nineteen different locations about the subject's scalp determined in accordance with the International 10-20 system can be substantial, often taking as long as thirty to forty-five minutes.
The chances of locating the electrodes in exactly the same positions on the scalp during repetitive testing is difficult, problematic and highly unlikely, thus rendering the reliability of results from repetitive tests somewhat suspect. Moreover, the chances of obtaining and maintaining good electrical contact with the scalp at all ninteen locations can prove difficult due to the differences in skull size and shape and the amount and texture of the hair of different subjects.
Against the foregoing background, it is a primary objective of the present invention to provide a headset unit which includes the plurality of electrodes required to conduct an EEG test.
It is another object of the present invention to provide such a headset which is adapted to locate and securely place said plurality of electrodes against the scalp of a subject undergoing such an EEG test.
It is still another objective of the present invention to provide such a headset which is able to repeatably locate and place the electrodes at substantially the same location on the subject's scalp in future testing.
It is yet another objective of the present invention to provide such a headset which is adapted to automatically introduce a conductive material between the electrode and the scalp.
It is still yet another objective of the present invention to provide such a headset where the electrodes can automatically adjust to accommodate subjects with scalps of different sizes and shapes.
It is still another objective of the present invention to provide such a headset which is adapted to provide a uniform force to the electrode independent of its positioning relative to the others.
It is yet still another objective of the present invention to provide such a headset which will afford the utilization of an electrolyte in the form of a water soluble gel rather than a sticky paste which can only be removed with great difficulty.